Method and device for enhancing VOIP security by selectively scrutinizing caller&#39;s geographical location

ABSTRACT

The VOIP call security is enhanced using the caller&#39;s geographical location information, which is transmitted to the home network device using an unmodifiable header. The home network device checks the veracity of the caller&#39;s geographical location information to determine whether the caller is suspicious.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a 35 U.S.C. § 371 National Stage of InternationalPatent Application No. PCT/SE2016/050771, filed Aug. 18, 2016,designating the United States.

TECHNICAL FIELD

Embodiments of the subject matter disclosed herein generally relate tomethods and devices for enhancing Voice Over Internet Protocol (VOIP)security, using caller's location information.

BACKGROUND

In the last couple of decades, the proliferation of mobile phones anddigital communications led to a spectacular increase in the number ofcalls. Simultaneously, fraudulent calls by various scammers have alsoincreased and became more sophisticated. We are all vulnerable, but somepeople (e.g., older persons or persons with disabilities) are morevulnerable than others.

Today, when receiving a call, a phone number is displayed on thecallee's phone. If the caller is a known contact, then the caller's nameis displayed in addition to or instead of the phone number. Situationsin which scammers deceivingly appear to be legitimate calls are known asspoofing attacks. For example, the caller appears to be callee's bankwhen in fact it is not. Such calls often originate from unlikelylocations, inconsistent with the alleged identity. Currently, there areno reliable techniques for ensuring or confirming that the caller is whohe/she pretends to be.

The most common transmission protocol, SIP (Session Initiation Protocol)offers a mechanism to track the path of a call across the network. InSIP, there is a header named “via”, which is used to track the visitednodes along the call's path. Since this header is optional and can beanonymized, it is not possible to rely that the caller's location iscorrectly identified using the “via” header.

A recently discussed Private Header (P-Header) extension to SIP(described in RFC7315 document of Internet Engineering Task Force, IETF,from July 2014) includes P-Visited-Network-IDs, which may reveal thecaller's location. A P-Visited-Network-ID indicates a visited networkdevice, which is an intermediate device transmitting messages betweenthe caller and the home network device (i.e., the network device thatconnects the call to the callee user equipment, UE). According toRFC7315, any visited network device inserts an identifier (i.e., aP-Visited-Network-ID) known by the home network device, in the P-Header.These identifiers should be globally unique, and may be a quoted textstring or a token. The home network device may use the identifiers toverify the existence of roaming agreements with the visited networkdevices, and to authorize the caller's registration.

This P-Visited-Network-ID approach has a number of drawbacks andlimitations. First, the granularity of the location information iscoarse, the P-Visited-Network-ID indicating location at a country level,instead of a province, city or even smaller divisions of a geographicalarea. Second, the P-Visited-Network-ID approach assumes that there aretrust relationships between the home network device and visited networkdevices. This is not always the case, since the P-header can be modifiedby a malicious visited network device. In other words, the maliciousvisited network device modifies one or more P-Visited-Network-IDs in theP-header. In order to prevent such modifications, all visited devicesshould apply a hop-by-hop integrity protection mechanism such as IPsec,or other available mechanisms. Given these drawbacks and limitations,this P-header based mechanism does not effectively provide the caller'slocation information in a way that is usable to identifying spoofingattacks.

It is desirable to find mechanisms for effectively enhancing VOIPsecurity by using accurate and reliable caller's location information.

SUMMARY

In order to enable a network to reject or to signal suspicious calls, amandatory header is implemented in the transmission protocol. Thismandatory header cannot be stripped from the associated message, and isadded by a trusted network element (e.g., the first network node thatthe message traverses). For example, in IMS SIP, this network node maybe the P-CSCF (proxy Call Session Control Function) of the user on theuser's initial REGISTER request.

According to an embodiment, there is a method performed by a networkoperator, for enhancing security of VOIP calls. The method includesdetermining whether a scrutiny of a caller is required when a call isinitiated. The method further includes, requesting the caller'sgeographical location information, if determined that the scrutiny isrequired, and checking veracity of the caller's geographical locationinformation to determine whether the caller is suspicious.

According to another embodiment there is network operator deviceconfigured to enhance security of VOIP calls having a communicationinterface and a processing unit. The communication interface isconfigured to exchange messages with other devices in a communicationnetwork. The processing unit, which includes at least one processor andis connected to the communication interface, is configured to determinewhether a scrutiny of a caller is required when a call is initiated, tocontrol the communication interface to request a caller's geographicallocation if the scrutiny is required, and to check veracity of thecaller's geographical location in order to determine whether the calleris suspicious.

According to yet another embodiment there is a network operator deviceconfigured to enhance security of VOIP calls having a logic module, aninformation demand module and a verification module. The logic moduledetermined whether a scrutiny of a caller is required. The informationdemand module requests caller's geographical location information whenthe logic module has determined that the scrutiny is required. Theverification module checks veracity of the caller's geographicallocation information to determine whether the caller is suspicious.

According to another embodiment, there is a client device in acommunication network having a communication interface configured tosend and receive messages from other devices in the communicationnetwork, and a data processing unit. The data processing unit, whichincludes at least one processor and is connected to the communicationinterface, is configured to control the communication interface to senda message with an unmodifiable header including geographical locationinformation of the client device, upon request.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate one or more embodiments and,together with the description, explain these embodiments. In thedrawings:

FIG. 1 is a flowchart of a method according to an embodiment;

FIG. 2 is a schematic diagram illustrating communications between acaller user equipment (UE), a network device, and a callee UE, accordingto an embodiment;

FIG. 3 is a schematic diagram of a network device according to anembodiment;

FIG. 4 is a block diagram of a network device according to anotherembodiment; and

FIG. 5 is a schematic representation of a client device according to anembodiment.

DETAILED DESCRIPTION

The following description of the embodiments refers to the accompanyingdrawings. The same reference numbers in different drawings identify thesame or similar elements. The following detailed description does notlimit the invention. Instead, the scope of the invention is defined bythe appended claims.

Reference throughout the specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with an embodiment is included in at least oneembodiment of the subject matter disclosed. Thus, the appearance of thephrases “in one embodiment” or “in an embodiment” in various placesthroughout the specification is not necessarily referring to the sameembodiment. Further, the particular features, structures orcharacteristics may be combined in any suitable manner in one or moreembodiments.

In some embodiments set forth below, the security of VOIP calls isenhanced by using the caller's geographical information obtained in areliable manner. The network device that connects the call to the calleeand/or the callee are enabled to better decide whether to forward,reject or answer the call. The network device may first evaluate whetherthe callee is vulnerable. This evaluation may be a default service foreveryone (since anyone may be a target of a spoofing attack) or anoptional service. The level of scrutiny employed in this evaluation maybe varied from a low scrutiny (e.g., triggered by a default service) toa higher scrutiny based on the callee's profile (i.e., the callee'sprofile may include an indication that a higher level of scrutiny hasbeen set). Old and/or disabled people are usually more vulnerable tospoofing attacks. A callee or his/her relatives can request that thenetwork operator to insert an indication that the callee is vulnerableinto the callee's profile.

If determined that the callee is vulnerable, the network device thenrequests the caller's geographical location information via anadditional header that cannot be modified by intermediate devices. Uponreceiving the additional header, the network device checks veracity ofthe caller's geographical location information. If the result of theveracity check is that the geographical location information istrustworthy, the network device may or may not present the geographicallocation information to the callee. If the result of the veracity checkis that the geographical location information is not trustworthy, thenetwork device warns the callee that the caller is suspicious.

The caller being suspicious is indicated to the callee's user equipment(UE) in order to reach the callee. If callee's UE is a modern UE, awarning and/or the caller's geographical location information can bedisplayed on the UE's screen. For older devices, a voice announcementand/or ringtone may be used to indicate a suspicious caller. In oneembodiment, the voice announcement may announce the caller'sgeographical location information.

In view of the above-discussed aspects, FIG. 1 is a flowchart of amethod 100 performed by a network operator, for enhancing security ofVOIP calls, according to an embodiment. Method 100 includes determiningwhether a scrutiny of the caller is required when a call is initiated atS110. Method 100 further includes requesting a caller's geographicallocation information, when determined that the scrutiny is required atS120, and checking veracity of the caller's geographical locationinformation to determine whether the caller is suspicious, at S130.These steps may be performed by a same physical device, or by two ormore intermediate devices, between the caller and the callee. Whilesteps S110 and S120 can easily be performed by any of the intermediatenodes, it seems favorable to perform S130 at the first node on thecaller side. Alternatively, S130 is performed by another node thatobtains information about the first node's location to enable theveracity check.

The scrutiny may be required if the callee's profile includes anindication for enhanced VOIP security service. This indication may beincluded in the callee's profile upon receiving an enhanced VOIPsecurity service request.

The scrutiny being required may alternatively or additionally bedetermined by analyzing a call detail record (CDR) of the caller. TheCDR is a data record that documents details related to a UE'scommunications. For example, the CDR includes time, duration, completionstatus, source number, and destination number for each call of the UE.Since the network operator owns CDR, network devices can analyze it. Theresult of the CDR analysis can be stored and/or shared.

Such CDR analysis may determine that scrutiny is required if caller'scalls have often been rejected by other callees and/or the caller'scalls frequently lasted less than a predetermined time interval (e.g.,30 s). Alternatively or additionally, the CDR analysis may determinethat the scrutiny is not required if the average duration of prior callsbetween the caller and the callee is longer than a predeterminedthreshold (e.g., 30 s).

Requesting the caller's geographical location information may triggerreceiving a reply message with the caller's geographical locationinformation included in an unmodifiable header.

If determined that the caller is suspicious at S130, the network devicemay then inform the callee before connecting the call, or may notconnect the call to the callee. Informing the callee may be achieved byforwarding the caller's geographical location information to the callee,sending an audio message to the callee prior to connecting the call,and/or activating a warning signal detectable by the callee.

Step S130, may include evaluating whether the caller's geographicallocation is in the same geographical area as a location of a firstnetwork operator node accessed to initiate the call. If the caller'sgeographical location is not in the same geographical area as the firstnetwork operator node's location, then the caller is suspicious. Thereare various sources from which a network operator device may acquire thefirst operator node's geographical location. For example, a node'sgeographical location may be using device's Location Area Identity(LAI). LAI is a unique number that identifies a particular location onEarth.

FIG. 2 illustrates communications between a caller UE 210, a networkdevice 220, and a callee UE 230 (time order of the illustratedoperations is from up to down), in a SIP environment. A new optional butun-modifiable header is enabled (i.e., to be generated and transmitted)in this SIP environment. This new header named, for example,“P-Origination-Location,” carries the caller's geographical locationinformation. This header may include a text string and may be generatedby the caller's UE upon receiving a request from its first network node.The first network node may perform a veracity check of this text string.

As illustrated in FIG. 2, first (at 1), the caller UE 210 sends an SIPINVITE message to initiate a VOIP call with the callee. Although in FIG.2, no visited devices are illustrated between the caller UE 210 and thenetwork device 220, such other devices may be present. The callee UE andthe network device may pertain to a different network than the callerUE.

Upon receiving the SIP INVITE message, the network device 220 determineswhether the callee is vulnerable at 2. Steps 3-11, which are labeled A1,follow if determined that the callee is vulnerable, and steps 12-14,which are labeled A2, follow if determined that the callee is notvulnerable. Determining that the callee is vulnerable triggersrequesting, generating and transmitting the P-Origination-Locationheader in the network. Thus, if the callee is vulnerable (A1), thenetwork device 220 sends SIP response 1xx to caller UE 210 requestingthe caller UE to provide P-Origination-Location header, at 3. Then, at4, the caller UE 210 sends an SIP UPDATE message including theP-Origination-Location header to the network device 220.

The network device 220 verifies the P-Origination-Location header'sveracity at 5. Steps 6-9, which are labeled B1, follow if veracity isconfirmed, and steps 10 and 11, which are labeled B2, follow if veracityis not confirmed. If the P-Origination-Location header's veracity isconfirmed (B1), the network device 220 replies by sending a “200 UPDATE”SIP message to the caller UE 210 at 6, and then responds to the initialSIP INVITE received at 1, by sending a “1xx INVITE” message to thecaller UE 210 at 7.

The network device 220 then sends a “SIP INVITE” message including the“P-Origination-Location” header to the callee UE 230 at 8. Uponreceiving this “SIP INVITE” message, the callee UE 230 conveys thecaller's location information from the P-Origination-Location header tothe callee, using the ringtone, a voice message and/or displaying thisinformation at 9. The known flow of the VOIP call then follows.

If the network device 220 determines that the P-Origination-Locationheader's veracity is not confirmed (B2), then the call is rejected bythe network device that sends a “4xx UPDATE” reject message at 10, and a“4xx INVITE” reject message at 11, to the caller UE 210. The networkdevice 220 may transmit an indication (e.g., a 0 value instead of avalid location) in the P-Origination-Location header if it has alreadydetermined that the caller is suspicious.

If at 2, the network device 220 determined that the callee is notvulnerable (A2), then the network device 220 sends a “1xx INVITE”message to the caller UE 210 at 12, and a “SIP INVITE” message to thecallee UE 230 at 13. Upon receiving the “SIP INVITE” message at 13, thecallee UE 230 produces the regular ringtone at 14.

The network device may perform an integrity check of theP-Origination-Location header received from the caller UE. For example,the network device may verify whether the geographical locationinformation provided by caller UE is in the same geographical area (likecity, or region) of the first traversed network node. The geographicalcoordinates of the first network node may be correlated to a specificarea of the city and country.

If callee UE is a smart phone, the geographical location information canbe displayed directly on the screen with the phone number. This type ofcallee UE may also indicate that the caller is suspicious if instead ofthe location information it has been received an indication that thecaller is suspicious (e.g., a “0” value). The smart phones may also usea special ring tone to signal a suspicious caller. If callee UE is anolder phone, then the network device may translate the geographicallocation information into an audio message causing the phone to play iteither as a ringtone or a voice announcement when the callee picks upthe call.

To summarize, the features that enable an enhanced VOIP security are:

-   -   an additional network header that is optional but non-modifiable        for VOIP applications;    -   the network device evaluates if the callee is vulnerable;    -   if determined that the callee is vulnerable, the network device        requests additional geographical location information of the        caller to check if caller is suspicious;    -   network device performs an integrity check of the geographical        location information    -   if integrity is confirmed, network device provides the        geographical location information to the callee.    -   if integrity is not confirmed, then the callee is informed that        the caller is suspicious.

FIG. 3 is a block diagram of a network device 300 including acommunication interface 310 and a processing unit 320. The communicationinterface is configured to exchange messages with other devices in acommunication network 312. The communication interface may receive amessage including the caller's geographical location information in anunmodifiable header.

The processing unit includes at least one processor and is connected tothe communication interface. The processing unit is configured todetermine whether a scrutiny of a caller is required when a call isinitiated, to control the communication interface to request a caller'sgeographical location information if the scrutiny is required, and tocheck veracity of the caller's geographical location information todetermine whether the caller is suspicious.

The processing unit may determine that the scrutiny is required if acallee's profile includes an indication that an enhanced VOIP securityis required. The data processing unit may have added this indication inthe callee's profile upon receiving a request. The processing unit maydetermine that the scrutiny is required if analyzing the CDR revealsthat caller's calls have often been rejected by other callees, or thatthe caller's calls have lasted frequently less than a predetermined timeinterval. Additionally, the processing unit may determine that thescrutiny is not required if analyzing the CDR reveals that prior callsbetween the caller and the callee lasted in average longer than apredetermined duration.

The processing unit may control the communication interface to informthe callee before connecting the call, or not connecting the call to thecallee, if the caller is suspicious. The communication interface mayinform the callee that the caller is suspicious by forwarding thecaller's geographical location to the callee, triggering an audiomessage prior to connecting the call, or activating a warning signal(e.g., a specific ringtone) detectable by the callee.

The processing unit may check the veracity by evaluating whether thecaller's geographical location is in a same geographical area as alocation of a first network operator node accessed to initiate the call.

Network operator device 300 may also include a memory 340 and anoperator interface 330. The memory may store executable codes which,when executed by the processing unit make the processing unit todetermine whether the scrutiny is required, to control the communicationinterface, and to check the veracity of the caller's geographicallocation information.

According to another embodiment, a network operator device 400 isillustrated in FIG. 4. This device is configured to enhance security ofVOIP calls and includes a logic module 410, an information demand module420 and a verification module 430. Logic module 410 determines whether ascrutiny of a caller is required, when a call is initiated. Informationdemand module 420 requests caller's geographical location informationwhen the logic module has determined that the scrutiny is required.Verification module 430 checks veracity of the caller's geographicallocation information to determine whether the caller is suspicious.

FIG. 5 illustrates a client device 500, which may operate as thecaller's phone. Device 500 includes a communication interface 510configured to send and receive messages from other devices in acommunication network, and a data processing unit 520. Data processingunit 520, which includes at least one processor and is connected to thecommunication interface, is configured to control the communicationinterface to send a message with an unmodifiable header (e.g., aP-Origination-Location header) including geographical locationinformation of the client device, upon request.

According to yet another embodiment, there is a network node configuredto serve client devices in a predetermined area. The network node mayhave the same structure as the device illustrated in FIG. 3. The networknode according to this embodiment is enabled to obtain its location anda range of an area it covers (i.e., the node is configured to providenetwork connectivity to devices within the covered area). The networknode may have a Global Positioning Satellite (GPS) module, which enablesit to identify its location. Alternatively, the network node's locationmay be a parameter provided by the network when setting up the networknode. The network may additionally also inform the network node aboutits coverage (for example, a circle whose center is the network node'slocation and radius is 100 km). The coverage may also be a configurableparameter.

Unlike conventional network nodes, upon receiving a connection requestfrom a device, this network node (the processing unit thereof) verifiesif the device's location information included in aP-Origination-Location header is within its service range. If thedevice's location information in the P-Origination-Location header isnot within the network node's service range, the network node may eitherreject the connection request, or forward the request with theP-Origination-Location header and an indication that the caller issuspicious.

The methods and devices described in this section enhance VOIP securityusing reliable caller geographic location information. The caller has toreveal its geographical location information. Having this informationmakes it more likely that a vulnerable person is warned to be cautious.For example, if a caller pretending to be your local bank is located ina different country, the callee is on notice. The caller's geographicallocation information may be transmitted using an SIP header that onceassociated with a message cannot be modified by visited network devices.

Thus, the embodiments disclosed in this section provide methods andnetwork devices that enhance security of VOIP calls based on reliablelocation information for the caller. It should be understood that thisdescription is not intended to limit the invention. On the contrary, theexemplary embodiments are intended to cover alternatives, modificationsand equivalents, which are included in the spirit and scope of theinvention. Further, in the detailed description of the exemplaryembodiments, numerous specific details are set forth in order to providea comprehensive understanding of the invention. However, one skilled inthe art would understand that various embodiments may be practicedwithout such specific details.

Although the features and elements of the present exemplary embodimentsare described in the embodiments in particular combinations, eachfeature or element can be used alone without the other features andelements of the embodiments or in various combinations with or withoutother features and elements disclosed herein. The methods or flowchartsprovided in the present application may be implemented in a computerprogram, software or firmware tangibly embodied in a computer-readablestorage medium for execution by a computer or a processor.

This written description uses examples of the subject matter disclosedto enable any person skilled in the art to practice the same, includingmaking and using any devices or systems and performing any incorporatedmethods. The patentable scope of the subject matter is defined by theclaims, and may include other examples that occur to those skilled inthe art. Such other examples are intended to be within the scope of theclaims.

What is claimed is:
 1. A method performed by a network operator, forenhancing security of a Voice Over Internet Protocol (VoIP) callinitiated by a calling device to a callee, the method comprising:receiving a first message transmitted by the calling device, wherein thefirst message indicates that the calling device is initiating the VoIPcall; determining whether a scrutiny of the call is required; as aresult of determining that a scrutiny of the call is required,requesting the calling device's geographical location information;receiving the requested geographical location information, wherein thereceived geographical location information identifies a statedgeographical location of the calling device; checking veracity of thereceived geographical location information to determine whether the callis suspicious, wherein checking the veracity of the receivedgeographical location information comprises: i) identifying a networknode that received the first message indicating that the calling deviceis initiating the VoIP call; ii) determining a geographical location ofthe network node; and iii) comparing the geographical location of thenetwork node with the stated geographic location of the calling device.2. The method of claim 1, wherein the scrutiny is required if thecallee's profile includes an indication for enhanced VOIP securityservice.
 3. The method of claim 2, further including: receiving arequest to include the indication for enhanced VOIP security in thecallee's profile.
 4. The method of claim 1, wherein whether the scrutinyis required is determined by analyzing a call detail record (CDR) of thecaller.
 5. The method of claim 4, wherein the analyzing of the CDRdetermines that the scrutiny is required if calls placed by the callerhave often been rejected by other callees and/or if calls placed by thecaller lasted frequently less than a predetermined time interval.
 6. Themethod of claim 4, wherein the analyzing of the CDR determines that thescrutiny is not required if prior calls between the caller and thecallee lasted longer than a predetermined duration.
 7. The method ofclaim 1, wherein the first message transmitted by the calling device isa Session Initiation Protocol (SIP) Invite message, and the step ofrequesting the calling device's geographical location informationcomprises transmitting to the calling device a SIP response message, andthe method further comprises receiving a SIP Update message transmittedby the calling device in reply to the SIP response message, the SIPUpdate message comprising a private header field comprising thegeographical location information that identifies the statedgeographical location of the calling device.
 8. The method of claim 1,further comprising: if the call is suspicious, informing the calleebefore connecting the call, or rejecting the call.
 9. The method ofclaim 8, wherein the informing is achieved by at least one of:forwarding the received geographical location information to the callee;sending an audio message to the callee prior to connecting the call,wherein the audio message comprises one of a voice announcement or aringtone; or activating a warning signal detectable by the callee,wherein the warning signal comprises one of a warning displayed on adevice of the callee or a display of the received geographical locationinformation on the device of the callee.
 10. A network operator deviceconfigured to enhance security of a Voice Over IP (VOIP) call initiatedby a calling device to a callee, the network operator device comprising:a receiver for receiving a first message transmitted by the callingdevice, wherein the first message indicates that the calling device isinitiating the VoIP call; and a processing unit that includes at leastone processor, wherein the network operator device is configured to:determine whether a scrutiny of the call is required; as a result ofdetermining that a scrutiny of the call is required, request the callingdevice's geographical location information; receive the requestedgeographical location information, wherein the received geographicallocation information identifies a stated geographical location of thecalling device; check veracity of the received geographical locationinformation to determine whether the call is suspicious, wherein thenetwork operator device is configured to check the veracity of thereceived geographical location information by performing a process thatcomprises: identifying a network node that received the first messageindicating that the calling device is initiating the VoIP call;determining a geographical location of the network node; and comparingthe geographical location of the network node with the stated geographiclocation of the calling device.
 11. The network operator device of claim10, wherein the scrutiny is required if the callee's profile includes anindication that an enhanced VOIP security is required.
 12. The networkoperator device of claim 11, wherein the processing unit adds theindication in the callee's profile upon receiving a request.
 13. Thenetwork operator device of claim 10, wherein the processing unitdetermines whether the scrutiny is required based on analyzing a calldetail record (CDR) of the caller.
 14. The network operator device ofclaim 13, wherein the processing unit determines that the scrutiny isrequired if analyzing the CDR reveals that caller's calls have oftenbeen rejected by other callees, or the caller's calls have lastedfrequently less than a predetermined time interval.
 15. The networkoperator device of claim 13, wherein the processing unit determines thatthe scrutiny is not required if analyzing the CDR reveals that priorcalls between the caller and the callee lasted in average longer than apredetermined duration.
 16. The network operator device of claim 10,wherein the first message transmitted by the calling device is a SessionInitiation Protocol (SIP) Invite message, and the network operatordevice is configured to request the calling device's geographicallocation information by transmitting to the calling device a SIPresponse message, and the network operator device is further configuredto receive a SIP Update message transmitted by the calling device inreply to the SIP response message, the SIP Update message comprising aprivate header field comprising the geographical location informationthat identifies the stated geographical location of the calling device.17. The network operator device of claim 10, wherein if the call issuspicious, the processing unit informs the callee before connecting thecall, sending a rejection message to the caller, or not connecting thecall to the callee.
 18. The network operator device of claim 17, whereinthe network operator device informs the callee that the caller issuspicious by at least one of: forwarding the received geographicallocation information to the callee; triggering an audio message prior toconnecting the call; or activating a warning signal detectable by thecallee.
 19. A method performed by a network operator for enhancingsecurity of Voice Over Internet Protocol (VoIP) call from a callingdevice operated by a caller to a called device operated by a callee, themethod comprising: receiving a first message transmitted by the callingdevice, wherein the first message indicates that the calling device isinitiating a VoIP call; receiving a second message transmitted by thecalling device, the second message comprising first geographic locationinformation, the first geographic location information identifying astated geographic location of the calling device; identifying a networknode that received the first message indicating that the calling deviceis initiating the VoIP call; determining a geographical location of thenetwork node; and comparing the stated geographic location of thecalling device with the determined geographical location of the networknode to determine whether the caller is suspicious; and as a result ofdetermining that the caller is suspicious, transmitting a call rejectionmessage to the calling device or informing the callee that the caller issuspicious, wherein obtaining the second geographic location informationindicating the actual geographic location of the calling devicecomprises obtaining network node information identifying the actualgeographic location of a network node that received the first messageindicating that the calling device is initiating the call.